Methods of screening for TRPM4b modulators

ABSTRACT

The invention relates, in part, to methods useful in identifying molecules, that bind TRPM4b, which modulate TRPM4b ion channel activity, and/or which alter expression of TRPM4b within cells. The TRPM4b channels as described herein contain TRPM4b polypeptides, which are in turn encoded by TRPM4b nucleic acids. The ion channels described herein are preferably formed in HEK-293 cells from one or more novel TRPM4b polypeptides, which exhibit one or more of the unique TRPM4b properties described herein.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.10/142,649, filed May 8, 2002, now U.S. Pat. No. 7,452,675, issued Nov.18, 2008; which claims priority to (1) U.S. provisional application Ser.No. 60/351,938, filed Jan. 25, 2002, entitled “LTRPC4 is aCA²⁺-Activated Non-Selective Cation Channel Mediating Cell MembraneDepolarization” and (2) U.S. provisional application Ser. No.60/377,937, filed May 2, 2002, entitled “Methods of Screening for TRPM4bModulators.”

FIELD OF THE INVENTION

The present invention relates to the use of a novel family ofCalcium-Activated Nonselective (“CAN”) transmembrane channelpolypeptides designated herein as “TRPM4b”.

BACKGROUND OF THE INVENTION

Ion channels are transmembrane multi-subunit proteins embedded in thecellular plasma membranes of living cells which permit the passage ofspecific ions from the extracellular side of the plasma membrane to theintracellular region of the cell. Specific ion transport is facilitatedby a central aqueous pore which is capable of opening and closing due tochanges in pore conformation. When the ion gate is open, ions flowfreely through the channel. When the ion gate is closed, ions areprevented from permeating the channel. Ion channels are found in amultitude of multicellular eukaryotic species and in a myriad ofdifferent cell types. Ion channels may be either voltage-gated orligand-gated. Channel gating is the process by which a particularchannel is either open or closed. An ion channel may be capable ofoccupying a range of different “open” or “closed” states. The gatingprocess may therefore require a particular sequence of transition statesor inclusion of alternative transition states before a channel attains aparticular level of gating. The gating process is modulated by asubstance or agent, which in some way alters or affects the manner inwhich the channel opens or closes. A channel may be gated by a ligandsuch as a neurotransmitter, an internal primary or secondary messenger,or other bioactive agent. The ligand either attaches to one or morebinding sites on the channel protein or attaches to a receptor that isassociated with the channel. If the channel is voltage-gated, changes inthe membrane potential trigger channel gating by conformational changesof charged elements within the channel protein. Whether a channel isligand-gated or voltage-gated, a change in one part of the channelproduces an effect in a different part of the channel which results inthe opening or closing of a permeant pathway.

The non-selective transmembrane channel polypeptides form a family ofcation channels comprised of seven members TRPC1-TRPC7. The channelproteins are further divided into three main subfamilies: S for Shortnonselective transmembrane channels, L for long non-selectivetransmembrane channels, and O for Osm-9-like non-selective transmembranechannels. Although the non-selective ion channel proteins are widelydistributed in mammalian tissues, the specific physiological propertiesof the channels remain largely unknown. The protein subunits of thenon-selective transmembrane channels have six transmembrane domainspredicted to assemble into tetramers for forming ionic channels. Theslightly hydrophobic amino acids which link the fifth and sixthtransmembrane domain are purported to line the pores of the channels.Amino terminal and carboxyl terminal domains of the non-selectiveprotein comprise the intracytoplasmic region of the channel. In spite ofsimilarities in structure, the functions of the non-selective channelproteins differ between members of the same polypeptide family. Studiesdemonstrate that each channel has a unique ion selectivity and aparticular mechanism for activation.

SUMMARY OF THE INVENTION

The invention relates to the use of a novel family of Calcium-ActivatedNonselective (“CAN”) transmembrane channel polypeptides designatedherein as “TRPM4b”. TRPM4b channels are specifically activated byelevations in cytoplasmic Ca²⁺ in the nanomolar range, may be directlygated by Ca²⁺, conduct monovalent cations such as Na⁺, K⁺, and Cs⁺without significant Ca²⁺ permeation, are activated subsequent toreceptor-mediated Ca²⁺-mobilization, support important cellularresponses such as neuronal bursting activity, kidney cell osmoticregulation and/or cardiac rhythmicity, regulate the magnitude ofCa²⁺-influx by modulating membrane potential and, in this manner, thedriving force for Ca²⁺ entry through other Ca²⁺-permeable pathways, andare not regulated by a voltage or Ca²⁺-dependent inactivation. Theinvention further relates to the use of recombinant nucleic acids thatencode TRPM4b and the methods of utilizing TRPM4b to bind candidatebioactive agents, for modulating TRPM4b activity, and for measuringTRPM4b permeability to monovalent cations. The invention further relatesto methods of modulating the cellular expression of the nucleic acidsthat encode TRPM4b.

One embodiment of the invention provides methods for screening forcandidate bioactive agents that bind to TRPM4b. In this method, TRPM4b,or a fragment thereof, is contacted with a candidate agent, and it isdetermined whether the candidate agent binds to TRPM4b. An embodiment ofthe invention provides for contacting TRPM4b with a library of two ormore candidate agents and then determining the binding of one or more ofthe candidate agents to TRPM4b. In a preferred embodiment, Ca²⁺ may bepresent in combination with one or more candidate agents.

In a further embodiment, TRPM4b comprises an ion channel and thecandidate agent(s) that bind the TRPM4b channel modulate the monovalentcationic permeability of the TRPM4b channel. In some embodiments, thecandidate agent(s) that bind TRPM4b, open the TRPM4b channel. In otherembodiments, the candidate agents that bind TRPM4b, close the TRPM4bchannel. In still other embodiments of the invention, the monovalentcations which permeate TRPM4b include Na⁺, K⁺, and Cs⁺.

In some embodiments the TRPM4b channel is in a recombinant cell whichcomprises a recombinant nucleic acid encoding TRPM4b, an induciblepromoter which is operably linked to the recombinant nucleic acid, and amonovalent cation indicator, such as fura-2. The recombinant cell isinduced to express TRPM4b and it is then contacted with a monovalentcation and a candidate agent. In another embodiment, the recombinantcell is contacted with a candidate agent prior to being contacted with amonovalent cation. Intracellular levels of the monovalent cation aredetected using the monovalent cation indicator. An embodiment of theinvention provides for contacting the recombinant cell with a monovalentcation solution comprising Na⁺, K⁺, and Cs⁺. In some embodiments, thecandidate agent increases the monovalent cation permeability of theTRPM4b channel. In other embodiments, the candidate agent decreases themonovalent cation permeability of the TRPM4b channel. In a preferredembodiment, the candidate agent alters the membrane potential of therecombinant cell by either increasing or decreasing monovalent cationpermeability of the TRPM4b channel. In another preferred embodiment, themonovalent cation indicator comprises a fluorescent molecule. In a morepreferable embodiment of the invention, the monovalent cation indicatorcomprises fura-2. In an alternate embodiment, the production of TRPM4bchannel is induced and the intracellular levels of monovalent cation aredetected in the presence of a candidate agent. That level is compared tothe intracellular level of monovalent cation detected in an uninducedrecombinant cell either in the presence or absence of a candidate agent.

It is another object of the invention to provide methods for measuringthe monovalent ion permeability of a TRPM4b channel. In this method, arecombinant cell is provided, which comprises a recombinant nucleic acidencoding TRPM4b, a promoter, either constitutive or inducible,preferably inducible, which is operably linked to the recombinantnucleic acid, and an intracellular cation indicator. The recombinantcell is contacted with a solution comprising a monovalent cation thatselectively interacts with the indicator to generate a signal.Intracellular levels of the monovalent cation are then measured whenTRPM4b is expressed by detecting the indicator signal. This measurementis compared to endogenous levels in which recombinant TRPM4b is notexpressed.

In a broader embodiment, the cell is not limited to a recombinant TRPM4bexpressing cell, but may comprise any cell capable of being used withany recombinantly expressed channel protein for determining agents whichmodulate the activity of the channel. The expression of the recombinantchannel is preferably under the control of an inducible promoter.

In a preferred embodiment the monovalent cation indicator comprises afluorescent molecule such as fura-2. In yet a further embodiment of theinvention the monovalent cation which selectively interacts with thecation indicator is Na⁺, K⁺, and Cs⁺. In some embodiments the modulatingactivity of a candidate bioactive agent which contacts the recombinantcell together with the monovalent cation agent increases the monovalentcation permeability of the TRPM4b channel, in others it decreases it. Ina further preferred embodiment, the modulating activity of the candidateagent alters the membrane potential of the recombinant cell by eitherincreasing or decreasing monovalent cation permeability of the TRPM4bchannel. In further embodiments the modulating activity of a candidatebioactive agent which contacts the recombinant cell prior to contactwith the monovalent cation agent increases the monovalent cationpermeability of the TRPM4b channel, in others it decreases it.

It is further an object of the invention to provide methods forscreening for candidate bioactive agents that are capable of modulatingexpression of TRPM4b. In this method, a recombinant cell is providedwhich is capable of expressing a recombinant nucleic acid encodingTRPM4b, a fragment thereof, including in some embodiments the 5′ and/or3′ expression regulation sequences normally associated with the TRPM4bgene. The recombinant cell is contacted with a candidate agent, and theeffect of the candidate agent on TRPM4b expression is determined. Insome embodiments, the candidate agent may comprise a small molecule,protein, polypeptide, or nucleic acid (e.g., antisense nucleic acid). Inanother embodiment of the invention, TRPM4b expression levels aredetermined in the presence of a candidate bioactive agent and theselevels are compared to endogenous TRPM4b expression levels. Thosecandidate agents which regulate TRPM4b expression can be tested innon-recombinant cells to determine if the same effect is reproduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B (SEQ ID No. 2) show the molecular characterization of TRPM4b.FIG. 1A depicts the schematic and primary structure of TRPM4b withamino-terminal unique region 1-4 (ATU), transmembrane domain regions(TM), coiled-coil region (CC). Underlined amino acids represent theN-terminal extension of TRPM4b; the rest of the sequence is identical tothe short splicing variant TRPM4. The amino acid sequence of TRPM4bprotein from amino acids 1 through 1214 (SEQ ID NO:2) is also shown.FIG. 1B depicts the Northern blot analysis of RNA from various tissuesand human cell lines using a specific TRPM4b antisense RNA probe. Celllines represent monocytes (U937), B lymphocytes (Ramos), T lymphocytes(Jurkat), basophils (Ku812), melanoma cells (G361) and embryonic kidneycells (HEK-293).

FIGS. 2A-C depict the biochemical analysis of TRPM4b. (A)Tetracycline-inducible expression of TRPM4b. Stable TRPM4b HEK-293clones were treated or not for 18 hr with 1 mg.ml-1 of tetracycline.Clones were analyzed for expression of a Flag-reactive protein byanti-Flag immunoprecipitation/anti-Flag immunoblotting. Ctrl indicatesimmunoprecipitation with an irrelevant antibody. (B) Surface expressionof TRPM4b. Surface proteins of tetracycline-induced clones were labeledwith iodine. TRPM4b was immunoprecipitated with the Flag antibody; thecell viability was tested by immunoprecipitation of the intracytoplasmicprotein Cbl. (C) TRPM4b homo-multimerization. HEK-293 cells wereco-transfected with two different tagged forms (V5 and Flag) of TRPM4bor co-transfected with TRPM4b VS-tagged and LTRPC2 Flag-tagged. Celllysates were immunoprecipitated with Flag and VS and Western blots ofthe immune complexes were probed with both anti-V5 and anti-Flagantibodies.

FIGS. 3A-E depict the functional expression of TRPM4b in HEK-293 cells.(A) Whole-cell recordings in HEK-293 cells overexpressing TRPM4b.Average inward and outward currents carried by TRPM4b at −80 and +80 mV,respectively. Cells were perfused with solutions in which [Ca²⁺]iclamped to either 300 nM (closed circles, n=5±s.e.m.) or 500 nM (opensquares, n=5±s.e.m). Arrow indicates the time at which the raw datatrace displayed in (B) was extracted. (B) Current-voltage relationshipunder experimental conditions as in (A), obtained 8 s after whole-cellestablishment from a representative cell perfused with 500 nM [Ca²⁺]i.Arrows indicate −80 and +80 mV, respectively. (C) Dose-response behaviorof expressed TRPM4b to various intracellular calcium concentrations.Data points represent average inward and outward currents at −80 and +80mV, respectively, taken 8 s after whole-cell establishment (n=3−5). (D)Receptor-mediated activation of expressed TRPM4b. Shown are concomitantmeasurements of global [Ca²⁺]i (bottom trace), whole-cell current(middle trace) and reversal potential (Erev) (top trace) in arepresentative cell (total n=8). For the time indicated, the cell wassuperfused with an extracellular solution containing 1 mM ATP. Holdingpotential was −60 mV to promote calcium influx. Note that TRPM4b currentamplitude does not strictly follow changes in [Ca²⁺]i and the initialrelease transient is less effective at activating TRPM4b than the laterphase of calcium influx. Symbols À and Á indicate the time at which rawdata traces displayed in (E) were extracted. (E) Current-voltagerelationships from the same cell as shown in (D). Both a control currenttrace before ATP challenge and a TRPM4b current trace (214 s afterwhole-cell establishment) are displayed.

FIGS. 4A-D depict the single channel properties of TRPM4b. (A)Activation of TRPM4b channels by 300 nM [Ca²⁺] recorded in inside-outpatches excised from TRPM4b-overexpressing HEK-293 cells. The patch wasexcised into a KCl-based solution in which [Ca²⁺]i was buffered to 300nM and the pipette solution was a NaCl-based standard external solution.Channel activity was measured at various membrane potentials asindicated. Data are from a single representative patch out of 17successful recordings. Note that open probability increases withpositive membrane voltage and single-channel amplitudes slightlyincrease at both positive and negative potentials. (B) Single-channelI-V relationship derived from averages of several events from differentpatches (n=2−5), yielding a single channel conductance of 25 pS between−60 mV and +60 mV. Note rectification of single-channel amplitudes atpositive and negative voltages. (C) Two sample single-channel ramprecordings measured under the conditions as in (A). Ramps spanned −100to +100 mV and were 5 s long. (D) Cumulative average of 129 singlechannel ramps (same patch as in (C)), consistent with the behavior ofwhole-cell currents carried by TRPM4b. Note the characteristic outwardrectification and Erev around 0 mV.

FIGS. 5A-E depict endogenous TRPM4b in HEK-293 cells. (A) Whole-cellrecordings in wild-type HEK-293 cells perfused with solutions in which[Ca²⁺]i clamped to 500 nM (n=3+s.e.m). Average inward and outwardcurrents at −80 and +80 mV, respectively, carried by endogenous currentswith TRPM4b characteristics. Arrow indicates the time at which the rawdata trace displayed in (B) was extracted. Note that activation ofendogenous TRPM4b proceeds slightly slower than overexpressedrecombinant TRPM4b. (B) Current-voltage relationship under experimentalconditions as in (A), obtained from a representative cell 200 s afterwhole-cell establishment. Arrows indicate −80 and +80 mV, respectively.(C) Dose-response behavior of expressed TRPM4b to various intracellularcalcium concentrations. Data points represent average inward and outwardcurrents at −80 and +80 mV, respectively, taken 200 s after whole-cellestablishment (n=3). (D) Receptor-mediated activation of endogenousTRPM4b. Shown are concomitant measurements of global [Ca²⁺]i (bottomtrace), whole-cell current (middle trace) and reversal potential (Erev)(top trace) in a representative cell (total n=8). For the timeindicated, the cell was superfused with an extracellular solutioncontaining 1 mM ATP. Holding potential was −60 mV to promote calciuminflux. Note the digital behavior of Erev switching between −80 mV and 0mM in dependence of TRPM4b activation (in a non voltage-clamped cell,the membrane potential will closely follow Erev). Note that TRPM4bcurrent amplitude does not strictly follow changes in [Ca²⁺]i and theinitial release transient is less effective at activating TRPM4b thanthe later phase of calcium influx. Symbols À and Á indicate the time atwhich raw data traces displayed in (E) were extracted. (E)Current-voltage relationships from the same cell as shown in (D). Both acontrol current trace before ATP challenge and a TRPM4b current trace(286 s after whole-cell establishment) are displayed.

FIGS. 6A-D depict that TRPM4b does not carry Ca²⁺ and inhibits Ca²⁺influx. (A) Whole-cell recordings in HEK-293 cells overexpressingTRPM4b. Average inward and outward currents carried by TRPM4b at −80 and+80 mV, respectively. Cells were perfused with solutions in which[Ca²⁺]i was buffered to 800 nM (n=5±s.e.m.). Cells were exposed to 120mM isotone CaC12 as indicated by the black bar (300 mOsm). Note thatinward currents are completely suppressed, suggesting that TRPM4b doesnot carry Ca²⁺ ions. (B) Current-voltage relationships of TRPM4bcurrents under experimental conditions as in (A) measured just beforeand during application of isotone CaCl2 (40 s after whole-cellestablishment). Note that isotone CaCl2 application changes Erev to −80mV and outward K+ currents remain largely unaffected. (C) Averaged[Ca²⁺]i signals in intact WT HEK-293 cells loaded with fura-2-AM andstimulated by the purinergic receptor agonist ATP (n=7−10). During thetime indicated by the bar, cells were exposed to 1 mM ATP in eitherNa⁺-based (+Na) or choline-based (−Na) extracellular solutions, asindicated by labels. (D) Same experimental protocol as in (C), exceptthat the measurements were performed on TRPM4b-overexpressing HEK-293cells (n=8−11).

FIG. 7 shows the recombinant nucleic acid molecule of a TRPM4b cDNAcomprised of nucleic acid sequences from 1 through about 4061 (SEQ IDNO:1).

FIG. 8 shows the amino acid sequence of a recombinant TRPM4b proteincomprised of sequences from 1 through about 1214 (SEQ ID NO:2).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates, in part, to methods useful in identifyingmolecules, that bind TRPM4b, which modulate TRPM4b ion channel activity,and/or which alter expression of TRPM4b within cells. The TRPM4bchannels as described herein comprise TRPM4b polypeptides, which are inturn encoded by TRPM4b nucleic acids. The ion channels described hereinare preferably formed in HEK293 cells and comprise one or more novelTRPM4b polypeptides, which exhibit one or more of the unique TRPM4bproperties described herein.

As described herein, the term “TRPM4b” refers to a member of the novelfamily of Ca²⁺ regulated transmembrane channel polypeptides. Thepolypeptides are also defined by their amino acid sequence, the nucleicacids which encode them, and the novel properties of TRPM4b. Such novelproperties include specific activation by elevations in cytoplasmic Ca²⁺in the nanomolar range, direct gating by Ca²⁺, conduction of monovalentcations such as Na⁺, K⁺, and Cs⁺ without significant Ca²⁺ permeation,activation subsequent to receptor-mediated Ca²⁺-mobilization, support ofimportant cellular responses such as neuronal bursting activity, kidneycell osmotic regulation and/or cardiac rhythmicity, regulation ofCa²⁺-influxes by modulation of membrane potential and, in this manner,the driving force for Ca²⁺ entry through other Ca²⁺-permeable pathways,and an absence of regulation by a voltage or Ca²⁺-dependentinactivation. Direct gating of the TRPM4b channel by Ca²⁺ appears tobegin when Ca²⁺ concentrations are within the 300 nM range.

The TRPM4b polypeptides and channels are fundamentally distinct from the“SOC” (Store Operated Channels) and “CRAC” (Calcium Release ActivatedChannels) polypeptides and channels, disclosed in “Characterization of aCalcium Family,” WO 00/40614, the disclosure of which is expresslyincorporated herein by reference. The SOC and CRAC proteins “may beactivated upon depletion of Ca²⁺ from intracellular calcium stores” (seeWO 00/40614 at page 2) and are further “subject to inhibition by highlevels of intracellular calcium” (see WO 00/40614 at page 10). TheTRPM4b channels of the invention, conversely, exhibit enhanced activityin the presence of high intracellular levels of calcium, may be directlygated by cytosolic Ca²⁺ concentrations in the nanomolar range, decreasethe driving force for Ca²⁺ influx through store operated Ca²⁺ channelsof non-excitable cells, are not influenced by depletion or reduction ofintracellular calcium stores, and operate to depolarize cell membranesin a Ca²⁺-dependent manner. SOC and CRAC are not regulated in thismanner.

The TRPM4b polypeptide is a novel member of the LTRPC family. Thespecific sequence disclosed herein as SEQ ID NO:2 (FIG. 8) was derivedfrom human kidney cells. However, TRPM4b is believed to be broadlyexpressed in various mammalian tissues, and is widely expressed in humantissues, with a dominant expression in the heart, placenta, andpancreas, as well as in the cell lines of the human hematopoetic system.

TRPM4b can be derived from natural sources or recombinantly modified tomake TRPM4b variants. The term “TRPM4b sequence” specificallyencompasses naturally-occurring truncated or secreted forms (e.g., anextracellular domain sequence), naturally-occurring variant forms (e.g.,alternatively spliced forms) and naturally-occurring allelic variants.The native sequence of the TRPM4b polypeptide from human kidney cells isa full-length or mature native sequence TRPM4b polypeptide comprisingamino acids from 1 through about 1214 of SEQ ID NO:2 (FIG. 8).

The TRPM4b polypeptide of the invention, or a fragment thereof, alsoincludes polypeptides having at least about 80% amino acid sequenceidentity, more preferably at least about 85% amino acid sequenceidentity, even more preferably at least about 90% amino acid sequenceidentity, and most preferably at least about 95% sequence identity withthe amino acid sequence of SEQ ID NO:2. Such TRPM4b polypeptidesinclude, for instance, TRPM4b polypeptides wherein one or more aminoacid residues are substituted and/or deleted, at the N- or C-terminus,as well as within one or more internal domains, of the sequence of SEQID NO:2. Those skilled in the art will appreciate that amino acidchanges may alter post-translational processes of the TRPM4b polypeptidevariant, such as changing the number or position of glycosylation sitesor altering the membrane anchoring characteristics. All TRPM4b proteins,however, exhibit one or more of the novel properties of the TRPM4bpolypeptides as defined herein.

“Percent (%) amino acid sequence identity” with respect to the TRPM4bpolypeptide sequences identified herein is defined as the percentage ofamino acid residues in a candidate sequence that are identical with theamino acid residues of SEQ ID NO:2 (FIG. 8), after aligning thesequences and introducing gaps, if necessary, to achieve the maximumpercent sequence identity, and not considering any conservativesubstitutions as part of the sequence identity. The % identity valuesused herein are generated by WU-BLAST-2 which was obtained from Altschulet al. Methods in Enzymology, 266:460-480 (1996);http://blast.wustl/edu/blast/README.html. WU-BLAST-2 uses several searchparameters, most of which are set to the default values. The adjustableparameters are set with the following values: overlap span=1, overlapfraction=0.125, word threshold (T)=11. The HSP S and HSP S2 parametersare dynamic values and are established by the program itself dependingupon the composition of the particular sequence and composition of theparticular database against which the sequence of interest is beingsearched, however, the values may be adjusted to increase sensitivity. A% amino acid sequence identity value is determined by the number ofmatching identical residues divided by the total number of residues ofthe “longer” sequence in the aligned region. The “longer” sequence isthe one having the most actual residues in the aligned region (gapsintroduced by WU-Blast-2 to maximize the alignment score are ignored).

In a further embodiment, the % identity values used herein are generatedusing a PILEUP algorithm. PILEUP creates a multiple sequence alignmentfrom a group of related sequences using progressive, pairwisealignments. It can also plot a tree showing the clustering relationshipsused to create the alignment. PILEUP uses a simplification of theprogressive alignment method of Feng & Doolittle, J. Mol. Evol.35:351-360 (1987); the method is similar to that described by Higgins &Sharp CABIOS 5:151-153 (1989). Useful PILEUP parameters including adefault gap weight of 3.00, a default gap length weight of 0.10, andweighted end gaps.

In yet another embodiment, TRPM4b polypeptides from humans or from otherorganisms may be identified and isolated using oligonucleotide probes ordegenerate polymerase chain reaction (PCR) primer sequences with anappropriate genomic or cDNA library. As will be appreciated by those inthe art, the TRPM4b unique nucleic acid sequence comprising nucleotidesequences of SEQ ID NO:1 (FIG. 7) encoding amino acids 1-174 of SEQ IDNO:2 (FIG. 8) or portions thereof, is particularly useful as a probeand/or PCR primer sequence. As is generally known in the art, preferredPCR primers are from about 15 to about 35 nucleotides in length, withfrom about 20 to about 30 being preferred, and may contain inosine asneeded. The conditions for the PCR reaction are well known in the art.

In a preferred embodiment, TRPM4b is a “recombinant protein” which ismade using recombinant techniques, i.e. through the expression of arecombinant TRPM4b nucleic acid. A recombinant protein is distinguishedfrom naturally occurring protein by at least one or morecharacteristics. For example, the protein may be isolated or purifiedaway from some or all of the proteins and compounds with which it isnormally associated in its wild type host, and thus may be substantiallypure. For example, an isolated protein is unaccompanied by at least someof the material with which it is normally associated in its naturalstate, preferably constituting at least about 0.5%, more preferably atleast about 5% by weight of the total protein in a given sample. Asubstantially pure protein comprises at least about 75% by weight of thetotal protein, with at least about 80% being preferred, and at leastabout 90% being particularly preferred. The definition includes theproduction of a protein from one organism in a different organism orhost cell. Alternatively, the protein may be made at a significantlyhigher concentration than is normally seen, through the use of aninducible promoter or high expression promoter, such that the protein ismade at increased concentration levels. Alternatively, the protein maybe in a form not normally found in nature, as in the addition of anepitope tag or of amino acid substitutions, additions and deletions, asdiscussed below.

In a further embodiment, TRPM4b variants may be recombinantly engineeredby replacing one amino acid with another amino acid having similarstructural and/or chemical properties, such as the replacement of aleucine with a serine, i.e., conservative amino acid replacements.

In a further embodiment substitutions, deletions, additions or anycombination thereof may be used to make TRPM4b variants. Generally thesechanges are done on a few amino acids to minimize the alteration of themolecule. However, larger changes may be tolerated in certaincircumstances. When small alterations in the characteristics of theTRPM4b polypeptide are desired, substitutions are generally made inaccordance with the following Table 1:

TABLE 1 Original Residue Exemplary Substitutions Ala Ser Arg Lys AsnGln, His Asp Glu Cys Ser Gln Asn Glu Asp Gly Pro His Asn, Gln Ile Leu,Val Leu Ile, Val Lys Arg, Gln, Glu Met Leu, Ile Phe Met, Leu, Tyr SerThr Thr Ser Trp Tyr Tyr Trp, Phe Val Ile, Leu

In a further embodiment, substantial changes in function or inimmunological identity are made by selecting substitutions that are lessconservative than those shown in Chart 1. For example, substitutions maybe made which more significantly affect: the structure of thepolypeptide backbone in the area of the alteration, for example thealpha-helical or beta-sheet structure; the charge or hydrophobicity ofthe molecule at the target site; or the bulk of the side chain. Thesubstitutions which in general are expected to produce the greatestchanges in the polypeptide's properties are those in which (a) ahydrophilic residue, e.g. seryl or threonyl is substituted for (or by) ahydrophobic residue, e.g. leucyl, isoleucyl, phenylalanyl, valyl oralanyl; (b) a cysteine or proline is substituted for (or by) any otherresidue; (c) a residue having an electropositive side chain, e.g.,lysyl, arginyl, or histidyl, is substituted for (or by) anelectronegative residue, e.g. glutamyl or aspartyl; or (d) a residuehaving a bulky side chain, e.g., phenylalanine, is substituted for (orby) one not having a side chain, e.g., glycine. The TRPM4b variants ofthis embodiment exhibit one or more properties of the TRPM4bpolypeptides originally defined herein.

In a further embodiment, the variants typically exhibit the samequalitative biological activity and will elicit the same immune responseas the naturally-occurring analogue, although variants also are selectedto modify the characteristics of the TRPM4b polypeptides as needed.Alternatively, the variant may be designed such that the biologicalactivity of the TRPM4b polypeptides is altered. For example,glycosylation sites may be altered or removed. The proteins encoded bythe nucleic acid variants exhibit at least one of the novel TRPM4bpolypeptide properties defined herein.

The proteins encoded by nucleic acid variants exhibit at least one ofthe novel TRPM4b polypeptide properties defined herein.

As used herein, “TRPM4b nucleic acids” or their grammatical equivalents,refer to nucleic acids, that encode TRPM4b polypeptides exhibiting oneor more of the novel TRPM4b polypeptide properties previously described.The TRPM4b nucleic acids exhibit sequence homology to SEQ ID NO:1(FIG.-7) where homology is determined by-comparing sequences or byhybridization assays.

A TRPM4b nucleic acid encoding a TRPM4b polypeptide is homologous to thecDNA forth in FIG. 7 (SEQ ID NO:1). Such TRPM4b nucleic acids arepreferably greater than about 75% homologous, more preferably greaterthan about 80%, more preferably greater than about 85% and mostpreferably greater than 90% homologous. In some embodiments the homologywill be as high as about 93 to 95 or 98%. Homology in this context meanssequence similarity or identity, with identity being preferred. Apreferred comparison for homology purposes is to compare the sequencecontaining sequencing differences to the known TRPM4b sequence. Thishomology will be determined using standard techniques known in the art,including, but not limited to, the local homology algorithm of Smith &Waterman, Adv. Appl. Math. 2:482 (1981), by the homology alignmentalgorithm of Needleman & Wunsch, J. Mol. Biol. 48:443 (1970), by thesearch for similarity method of Pearson & Lipman, PNAS USA 85:2444(1988), by computerized implementations of these algorithms (GAP,BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package,Genetics Computer Group, 575 Science Drive, Madison, Wis.), the Best Fitsequence program described by Devereux et al., Nucl Acid Res. 12:387-395(1984), preferably using the default settings, or by inspection.

In a preferred embodiment, the % identity values used herein aregenerated using a PILEUP algorithm. PILEUP creates a multiple sequencealignment from a group of related sequences using progressive, pairwisealignments. It can also plot a tree showing the clustering relationshipsused to create the alignment. PILEUP uses a simplification of theprogressive alignment method of Feng & Doolittle, J. Mol. Evol.35:351-360 (1987); the method is similar to that described by Higgins &Sharp CABIOS 5:151-153 (1989). Useful PILEUP parameters including adefault gap weight of 3.00, a default gap length weight of 0.10, andweighted end gaps.

In preferred-embodiment, a BLAST algorithm is used. BLAST is describedin Altschul et al., J. Mol. Biol. 215:403-410, (1990) and Karlin et al.,PNAS USA 90:5873-5787 (1993). A particularly useful BLAST program is theWU-BLAST-2, obtained from Altschul et al., Methods in Enzymology,266:460-480 (1996); http://blast.wustl/edu/blast/README.html. WU-BLAST-2uses several search parameters, most of which are set to the defaultvalues. The adjustable parameters are set with the following values:overlap span=1, overlap fraction=0.125, word threshold (T)=11. The HSP Sand HSP S2 parameters are dynamic values and are established by theprogram itself depending upon the composition of the particular sequenceand composition of the particular database against which the sequence ofinterest is being searched; however, the values may be adjusted toincrease sensitivity. A % amino acid sequence identity value isdetermined by the number of matching identical residues divided by thetotal number of residues of the “longer” sequence in the aligned region.The “longer” sequence is the one having the most actual residues in thealigned region (gaps introduced by WU-Blast-2 to maximize the alignmentscore are ignored).

In a preferred embodiment, “percent (%) nucleic acid sequence identity”is defined as the percentage of nucleotide residues in a candidatesequence that are identical with the nucleotide residue sequences of SEQID NO:1 (FIG. 7). A preferred method utilizes the BLASTN module ofWU-BLAST-2 set to the default parameters, with overlap span and overlapfraction set to 1 and 0.125, respectively.

The alignment may include the introduction of gaps in the sequences tobe aligned. In addition, for sequences which contain either more orfewer nucleosides than those of SEQ ID NO:1 (FIG. 7), it is understoodthat the percentage of homology will be determined based on the numberof homologous nucleosides in relation to the total number ofnucleosides. Thus, for example, homology of sequences shorter than thoseof the sequences identified herein and as discussed below, will bedetermined using the number of nucleosides in the shorter sequence.

As described above, the TRPM4b nucleic acids can also be defined byhomology as determined through hybridization studies. Hybridization ismeasured under low stringency conditions, more preferably under moderatestringency conditions, and most preferably, under high stringencyconditions. The proteins encoded by such homologous nucleic acidsexhibit at least one of the novel TRPM4b polypeptide properties definedherein. Thus, for example, nucleic acids which hybridize under highstringency to a nucleic acid having the sequence set forth as SEQ IDNO:1 (FIG. 7) and their complements, are considered TRPM4b nucleic acidsequences providing they encode a protein having a TRPM4b property.

“Stringency” of hybridization reactions is readily determinable by oneof ordinary skill in the art, and generally is an empirical calculationdependent upon probe length, washing temperature, and saltconcentration. In general, longer probes require higher temperatures forproper annealing, while shorter probes need lower temperatures.Hybridization generally depends on the ability of denatured DNA toreanneal when complementary strands are present in an environment belowtheir melting temperature. The higher the degree of desired homologybetween the probe and hybridizable sequence, the higher the relativetemperature which can be used. As a result, it follows that higherrelative temperatures would tend to make the reaction conditions morestringent, while lower temperatures less so. For additional examples ofstringency of hybridization reactions, see Ausubel et al., CurrentProtocols in Molecular Biology, Wiley Interscience Publishers, (1995).

“Stringent conditions” or “high stringency conditions”, as definedherein, may be identified by those that: (1) employ low ionic strengthand high temperature for washing, for example 0.015 M sodiumchloride/0.0015 M sodium citrate/0.1% sodium dodecyl sulfate at 50° C.;(2) employ during hybridization a denaturing agent, such as formamide,for example, 50% (v/v) formamide with 0.1% bovine serum albumin/0.1%Fico11/0.1% polyvinylpyrrolidone/50 m.M sodium phosphate buffer at pH6.5 with 750 mM sodium chloride, 75 mM sodium citrate at 42° C.; or (3)employ 50% formamide, 5×SSC (0.75 M NaCl, 0.075 M sodium citrate), 50 mMsodium phosphate (pH 6.8), 0.1% sodium pyrophosphate, 5×Denhardt'ssolution, sonicated salmon sperm DNA (50 μg/ml), 0.1% SDS, and 10%dextran sulfate at 42° C., with washes at 42° C. in 0.2×SSC (sodiumchloride/sodium citrate) and 50% formamide at 55° C., followed by ahigh-stringency wash consisting of 0.1×SSC containing EDTA at 55° C.

“Moderately stringent conditions” may be identified as described bySambrook et al., Molecular Cloning: A Laboratory Manual, New York: ColdSpring Harbor Press, 1989, and include the use of washing solution andhybridization conditions (e.g., temperature, ionic strength and % SDS)less stringent that those described above. An example of moderatelystringent conditions is overnight incubation at 37° C. in a solutioncomprising: 20% formamide, 5×SSC (150 mM NaCl, 15 mM trisodium citrate),50 mM sodium phosphate (pH 7.6), 5×Denhardt's solution, 10% dextransulfate, and 20 mg/mL denatured sheared salmon sperm DNA, followed bywashing the filters in 1×SSC at about 37-50° C. The skilled artisan willrecognize how to adjust the temperature, ionic strength, etc. asnecessary to accommodate factors such as probe length and the like.Generally, stringent conditions are selected to be about 5-10° C. lowerthan the thermal melting point (Tm) for the specific sequence at adefined ionic strength pH. The Tm is the temperature (under definedionic strength, pH and nucleic acid concentration) at which 50% of theprobes complementary to the target hybridize to the target sequence atequilibrium (as the target sequences are present in excess, at Tm, 50%of the probes are occupied at equilibrium). Stringent conditions will bethose in which the salt concentration is less than about 1.0 M sodiumion, typically about 0.01 to 1.0 M sodium ion concentration (or othersalts) at pH 7.0 to 8.3 and the temperature is at least about 30° C. forshort probes (e.g., 10 to 50 nucleotides) and at least about 60° C. forlong probes (e.g., greater than 50 nucleotides). Stringent conditionsmay also be achieved with the addition of destabilizing agents such asformamide.

In another embodiment, less stringent hybridization conditions are used;for example, moderate or low stringency conditions may be used, as areknown in the art. For additional details regarding stringency ofhybridization reactions, see Ausubel et al., Current Protocols inMolecular Biology, Wiley Interscience Publishers, (1995).

The TRPM4b nucleic acids, as defined herein, may be single stranded ordouble stranded, as specified, or contain portions of both doublestranded or single stranded sequence. As will be appreciated by those inthe art, the depiction of a single strand (“Watson”) also defines thesequence of the other strand (“Crick”); thus the sequences describedherein also include the complement of the sequence. The nucleic acid maybe DNA, both genomic and cDNA, RNA or a hybrid, where the nucleic acidcontains any combination of deoxyribo- and ribo-nucleotides, and anycombination of bases, including uracil, adenine, thymine, cytosine,guanine, inosine, xanthine hypoxanthine, isocytosine, isoguanine, etc.As used herein, the term “nucleoside” includes nucleotides andnucleoside and nucleotide analogs, and modified nucleosides such asamino modified nucleosides. In addition, “nucleoside” includesnon-naturally occurring analog structures. Thus for example theindividual units of a peptide nucleic acid, each containing a base, arereferred to herein as a nucleoside.

The TRPM4b nucleic acids, as defined herein, are recombinant nucleicacids. By the term “recombinant nucleic acid” herein is meant nucleicacid, originally formed in vitro, in general, by the manipulation ofnucleic acid by polymerases and endonucleases, in a form not normallyfound in nature. Thus an isolated nucleic acid, in a linear form, or anexpression vector formed in vitro by ligating DNA molecules that are notnormally joined, are both considered recombinant for the purposes ofthis invention. It is understood that once a recombinant nucleic acid ismade and reintroduced into a host cell or organism, it will replicatenon-recombinantly, i.e., using the in vivo cellular machinery of thehost cell rather than in vitro manipulations; however, such nucleicacids, once produced recombinantly, although subsequently replicatednonrecombinantly, are still considered-recombinant for the purposes ofthe invention. Homologs and alleles of the TRPM4b nucleic acid moleculesare included in the definition.

The recombinant cDNA nucleic acid (SEQ ID NO:1) encoding a TRPM4bprotein (SEQ ID NO:2), or portions thereof, may be used as hybridizationprobes for a cDNA library to isolate the full-length TRPM4b gene fromother multicellular eukaryotic species, or to isolate still other genes(for instance, those encoding naturally-occurring variants of the TRPM4bpolypeptide or the TRPM4b polypeptide from other multicellulareukaryotic species) which have a desired sequence identity to aparticular TRPM4b nucleotide coding sequence. Optionally, the length ofthe probes will be about 20 through about 50 bases. The hybridizationprobes may be derived from the nucleotide sequences of SEQ ID NO:1 orfrom genomic sequences including promoters, enhancer elements andintrons of particular native nucleotide sequences of TRPM4b. By way ofexample, a screening method will comprise isolating the coding region ofa TRPM4b gene using the known DNA sequence to synthesize a selectedprobe of about 40 bases.

Hybridization probes may be labeled by a variety of labels, includingradionucleotides such as ³²P or ³⁵S or enzymatic labels such as alkalinephosphatase coupled to the probe via avidin/biotin coupling systems.Labeled probes having a sequence complementary to that of the TRPM4bgene of the invention can be used to screen libraries of human cDNA,genomic DNA or mRNA to determine which members of such libraries theprobe hybridizes to. Hybridization have been previously described below.

The probes may also be employed in PCR techniques to generate a pool ofsequences for identification of closely related TRPM4b nucleotide codingsequences. Nucleotide sequences encoding TRPM4b polypeptides can also beused to construct hybridization probes for mapping the gene whichencodes that TRPM4b and for the genetic analysis of individuals withgenetic disorders. The nucleotide sequences provided herein may bemapped to a chromosome and specific regions of a chromosome using knowntechniques, such as in situ hybridization, linkage analysis againstknown chromosomal markers, and hybridization screening with libraries.

In another embodiment, DNA encoding the TRPM4b polypeptide may beobtained from a cDNA library prepared from tissue believed to possessthe TRPM4b mRNA and to express it at a detectable level. Accordingly,human TRPM4b DNA can be conveniently obtained from a cDNA libraryprepared from human tissue, or a cDNA kidney library prepared from humankidney tissue. The TRPM4b-encoding gene may also be obtained from amulticellular eukaryotic genomic library or by oligonucleotidesynthesis.

Libraries can be screened with probes (such as antibodies to TRPM4b DNAor oligonucleotides of at least about 20-80 bases) designed to identifythe gene of interest or the protein encoded by it. Screening the cDNA orgenomic library with the selected probe may be conducted using standardprocedures, such as described in Sambrook et al., Molecular Cloning: ALaboratory Manual (New York: Cold Spring Harbor Laboratory Press, 1989).An alternative means to isolate the gene encoding TRPM4b is to use PCRmethodology [Sambrook et al., supra; Dieffenbach et al., PCR Primer: ALaboratory Manual (Cold Spring Harbor Laboratory Press, 1995)].

The examples below describe techniques for screening a cDNA library. Theoligonucleotide sequences selected as probes should be of sufficientlength and sufficiently unambiguous that false positives are minimized.The oligonucleotide is preferably labeled such that it can be detectedupon hybridization to DNA in the library being screened. Methods oflabeling are well known in the art, and include the use of radiolabelslike ³²P-labeled ADPR, biotinylation or enzyme labeling. Hybridizationconditions, including moderate stringency and high stringency, areprovided in Sambrook et al., supra, and have been described previously.

Sequences identified in such library screening methods can be comparedand aligned to other known sequences deposited and available in publicdatabases such as GenBank or other private sequence databases. Sequenceidentity (at either the amino acid or nucleotide level) within definedregions of the molecule or across the full-length sequence can bedetermined through sequence alignment using computer software programssuch as ALIGN, DNAstar, BLAST, BLAST2 and INHERIT which employ variousalgorithms to measure homology, as has been previously described.

Nucleic acid encoding TRPM4b polypeptides, as defined herein, may beobtained by screening selected cDNA or genomic libraries using all orpart of the nucleotide sequences of SEQ ID NO:1 (FIG. 7). Conventionalprimer extension procedures as described in Sambrook et al., supra, areused to detect precursors and processing intermediates of mRNA that maynot have been reverse-transcribed into cDNA.

Nucleotide sequences (or their complement) encoding the TRPM4bpolypeptides have various applications in the art of molecular biology,including uses as hybridization probes, in chromosome and gene mapping,and in the generation of anti-sense RNA and DNA.

In another embodiment, the TRPM4b nucleic acids, as defined herein, areuseful in a variety of applications, including diagnostic applications,which will detect naturally occurring TRPM4b nucleic acids, as well asscreening applications; for example, biochips comprising nucleic acidprobes to the TRPM4b nucleic acids sequences can be generated. In thebroadest sense, then, by “nucleic acid” or “oligonucleotide” orgrammatical equivalents herein means at least two nucleotides covalentlylinked together.

In another embodiment, the TRPM4b nucleic acid sequence of SEQ ID NO:1(FIG. 7), as described above, is a cDNA fragment of a larger gene, i.e.it is a nucleic acid segment. “Genes” in this context include codingregions, non-coding regions, and mixtures of coding and non-codingregions. Accordingly, as will be appreciated by those in the art, usingthe sequences provided herein, additional sequences of TRPM4b genes canbe obtained, using techniques well known in the art for cloning eitherlonger sequences or the full length sequences; see Maniatis et al., andAusubel, et al., supra, hereby expressly incorporated by reference.

Once the TRPM4b nucleic acid, as described above, is identified, it canbe cloned and, if necessary, its constituent parts recombined to formthe entire TRPM4b gene. Once isolated from its natural source, e.g.contained within a plasmid or other vector or excised therefrom as alinear nucleic acid segment, the recombinant TRPM4b nucleic acid can befurther used as a probe to identify and isolate other TRPM4b nucleicacids, from other multicellular eukaryotic organisms, for exampleadditional coding regions. It can also be used as a “precursor” nucleicacid to make modified or variant TRPM4b nucleic acids.

In another embodiment, the TRPM4b nucleic acid (e.g., cDNA or genomicDNA), as described above, encoding the TRPM4b polypeptide may beinserted into a replicable vector for cloning (amplification of the DNA)or for expression. Various vectors are publicly available. The vectormay, for example, be in the form of a plasmid, cosmid, viral particle,or phage. The appropriate nucleic acid sequence may be inserted into thevector by a variety of procedures. In general, DNA is inserted into anappropriate restriction endonuclease site(s) using techniques known inthe art. Vector components generally include, but are not limited to,one or more of a signal sequence, an origin of replication, one or moremarker genes, an enhancer element, a promoter, and a transcriptiontermination sequence. Construction of suitable vectors containing one ormore of these components employs standard ligation techniques which areknown to the skilled artisan.

A host cell comprising such a vector is also provided. By way ofexample, the host cells may be mammalian host cell lines which includeChinese hamster ovary (CHO), COS cells, cells isolated from human bonemarrow, human spleen or kidney cells, cells isolated from human cardiactissue, human pancreatic cells, and human leukocyte and monocyte cells.More specific examples of host cells include monkey kidney CV1 linetransformed by SV40 (COS-7, ATCC CRL 1651); human embryonic kidney line(293 or 293 cells subcloned for growth in suspension culture, Graham etal., J. Gen Virol., 36:59 (1977)); Chinese hamster ovarycells/-DHFR(CHO, Urlaub and ChasM, Proc. Natl. Acad. Sci. USA, 77:4216(1980)); human pancreatic β-cells; mouse sertoli cells (TM4, Mather,Biol. Reprod., 23:243-251 (1980)); human lung cells (W138, ATCC CCL 75);human liver cells (Hep G2, HB 8065); and mouse mammary tumor cells (MMT060562, ATCC CCL51). The selection of the appropriate host cell isdeemed to be within the skill in the art. In the preferred embodiment,HEK-293 cells are used as host cells. A process for producing TRPM4bpolypeptides is further provided and comprises culturing host cellsunder conditions suitable for expression of the TRPM4b polypeptide andrecovering the TRPM4b polypeptide from the cell culture.

In another embodiment, expression and cloning vectors are used whichusually contain a promoter, either constitutive or inducible, that isoperably linked to the TRPM4b-encoding nucleic acid sequence to directmRNA synthesis. Promoters recognized by a variety of potential hostcells are well known. The transcription of a TRPM4b DNA encoding vectorin mammalian host cells is preferably controlled by an induciblepromoter, for example, by promoters obtained from heterologous mammalianpromoters, e.g. the actin promoter or an immunoglobulin promoter, andfrom heat-shock promoters. Examples of inducible promoters which can bepracticed in the invention include the hsp 70 promoter, used in eithersingle or binary systems and induced by heat shock; the metallothioneinpromoter, induced by either copper or cadmium (Bonneton et al., FEBSLett. 1996 380(1-2): 33-38); the Drosophila opsin promoter, induced byDrosophila retinoids (Picking, et al., Experimental Eye Research, 199765(5): 717-27); and the tetracycline-inducible full CMV promoter. Of allthe promoters identified, the tetracycline-inducible full CMV promoteris the most preferred. Examples of constitutive promoters include theGAL4 enhancer trap lines in which expression is controlled by specificpromoters and enhancers or by local position effects; and thetransactivator-responsive promoter, derived from E. coli, which may beeither constitutive or induced, depending on the type of promoter it isoperably linked to.

Transcription of a DNA encoding the TRPM4b by higher eukaryotes may beincreased by inserting an enhancer sequence into the vector. Enhancersare cis-acting elements of DNA, usually about from 10 to 300 bp, thatact on a promoter to increase its transcription. Many enhancer sequencesare now known from mammalian genes (globin, elastase, albumin,α-fetoprotein, and insulin). Typically, however, one will use anenhancer from a eukaryotic cell virus. Examples include the SV40enhancer on the late side of the replication origin (bp 100-270), thecytomegalovirus early promoter enhancer, the polyoma enhancer on thelate side of the replication origin, and adenovirus enhancers. Theenhancer may be spliced into the vector at a position 5′ or 3′ to theTRPM4b coding sequence, but is preferably located at a site 5′ from thepromoter.

The methods of the invention utilize TRPM4b polypeptides or nucleicacids which encode TRPM4b polypeptides for identifying candidatebioactive agents which bind to TRPM4b, which modulate the activity ofTRPM4b ion channels, or which alter the expression of TRPM4b withincells.

The term “candidate bioactive agent” as used herein describes anymolecule which binds to TRPM4b, modulates the activity of a TRPM4b ionchannel, and/or alters the expression of TRPM4b within cells. Amolecule, as described herein, can be an oligopeptide, small organicmolecule, polysaccharide, polynucleotide, or multivalent cation etc.Generally a plurality of assay mixtures are run in parallel withdifferent agent concentrations to obtain a differential response to thevarious concentrations. Typically, one of these concentrations serves asa negative control, i.e., at zero concentration or below the level ofdetection.

Candidate agents encompass numerous chemical classes, though typicallythey are multivalent cations or organic molecules, or small organiccompounds having a molecular weight of more than 100 and less than about2,500 daltons (D). Preferred small molecules are less than 2000, or lessthan 1500 or less than 1000 or less than 500 D. Candidate agentscomprise functional groups necessary for structural interaction withproteins, particularly hydrogen bonding, and typically include at leastan amine, carbonyl, hydroxyl or carboxyl group, preferably at least twoof the functional chemical groups. The candidate agents often comprisecyclical carbon or heterocyclic structures and/or aromatic orpolyaromatic structures substituted with one or more of the abovefunctional groups. Candidate agents are also found among biomoleculesincluding peptides, saccharides, fatty acids, steroids, purines,pyrimidines, derivatives, structural analogs or combinations thereof.Particularly preferred are peptides.

Candidate agents are obtained from a wide variety of sources includinglibraries of synthetic or natural compounds. For example, numerous meansare available for random and directed synthesis of a wide variety oforganic compounds and biomolecules, including expression of randomizedoligonucleotides. Alternatively, libraries of natural compounds in theform of plant and animal extracts are available or readily produced.Additionally, natural or synthetically produced libraries and compoundsare readily modified through conventional chemical, physical andbiochemical means. Known pharmacological agents may be subjected todirected or random chemical modifications, such as acylation,alkylation, esterification, amidification to produce structural analogs.

In a preferred embodiment, the candidate bioactive agents are proteins.By “protein” herein is meant at least two covalently attached aminoacids, which includes proteins, polypeptides, oligopeptides andpeptides. The protein may be made up of naturally occurring amino acidsand peptide bonds, or synthetic peptidomimetic structures. Thus “aminoacid”, or “peptide residue”, as used herein means both naturallyoccurring and synthetic amino acids. For example, homo-phenylalanine,citrulline and noreleucine are considered amino acids for the purposesof the invention. “Amino acid” also includes imino acid residues such asproline and hydroxyproline. The side chains may be in either the (R) orthe (S) configuration. In the preferred embodiment, the amino acids arein the (S) or L-configuration. If non-naturally occurring side chainsare used, non-amino acid substituents may be used, for example toprevent or retard in vivo degradations.

In a preferred embodiment, the-candidate bioactive agents are naturallyoccurring proteins or fragments of naturally occurring proteins. Thus,for example, cellular extracts containing proteins, or random ordirected digests of proteinaceous cellular extracts, may be used. Inthis way libraries of multicellular eucaryotic proteins may be made forscreening in the methods of the invention. Particularly preferred inthis embodiment are libraries of multicellular eukaryotic proteins, andmammalian proteins, with the latter being preferred, and human proteinsbeing especially preferred.

In a preferred embodiment, the candidate bioactive agents are peptidesof from about 5 to about 30 amino acids, with from about 5 to about 20amino acids being preferred, and from about 7 to about 15 beingparticularly preferred. The peptides may be digests of naturallyoccurring proteins as is outlined above, random peptides, or “biased”random peptides. By “randomized” or grammatical equivalents herein ismeant that each nucleic acid and peptide consists of essentially randomnucleotides and amino acids, respectively. Since generally these randompeptides (or nucleic acids, discussed below) are chemically synthesized,they may incorporate any nucleotide or amino acid at any position. Thesynthetic process can be designed to generate randomized proteins ornucleic acids, to allow the formation of all or most of the possiblecombinations over the length of the sequence, thus forming a library ofrandomized candidate bioactive proteinaceous agents.

In one embodiment, the library is fully randomized, with no sequencepreferences or constants at any position. In a preferred embodiment, thelibrary is biased. That is, some positions within the sequence areeither held constant, or are selected from a limited number ofpossibilities. For example, in a preferred embodiment, the nucleotidesor amino acid residues are randomized within a defined class, forexample, of hydrophobic amino acids, hydrophilic residues, stericallybiased (either small or large) residues, towards the creation of nucleicacid binding domains, the creation of cysteines, for cross-linking,prolines for SH-3 domains, serines, threonines, tyrosines or histidinesfor phosphorylation sites, etc., or to purines, etc.

In a preferred embodiment, the candidate bioactive agents are nucleicacids.

As described above generally for proteins, nucleic acid candidatebioactive agents may be naturally occurring nucleic acids, randomnucleic acids, or “biased” random nucleic acids. For example, digests ofprocaryotic or eucaryotic genomes may be used as is outlined above forproteins.

In a preferred embodiment, the candidate bioactive agents are organicchemical moieties, a wide variety of which are available in theliterature.

In a preferred embodiment, anti-sense RNAs and DNAs can be used astherapeutic agents for blocking the expression of certain TRPM4b genesin vivo. It has already been shown that short antisense oligonucleotidescan be imported into cells where they act as inhibitors, despite theirlow intracellular concentrations caused by their restricted uptake bythe cell membrane. (Zamecnik et al., (1986), Proc. Natl. Acad. Sci. USA83:4143-4146). The anti-sense oligonucleotides can be modified toenhance their uptake, e.g. by substituting their negatively chargedphosphodiester groups by uncharged groups. In a preferred embodiment,TRPM4b anti-sense RNAs and DNAs can be used to prevent TRPM4b genetranscription into mRNAs, to inhibit translation of TRPM4b mRNAs intoproteins, and to block activities of preexisting TRPM4b proteins.

As used herein, a monovalent cation indicator is a molecule that isreadily permeable to a cell membrane or otherwise amenable to transportinto a cell e.g., via liposomes, etc., and upon entering a cell,exhibits a fluorescence that is either enhanced or quenched upon contactwith a monovalent cation. Examples of monovalent cation indicatorsuseful in the invention are set out in Haugland, R. P. Handbook ofFluorescent Probes and Research Chemicals. , 6th ed. Molecular Probes,Inc Eugene, Oreg., pp. 504-550 (1996);

incorporated herein by reference in its entirety.

In a preferred embodiment for binding assays, either TRPM4b or thecandidate bioactive agent is labeled with, for example, a fluorescent, achemiluminescent, a chemical, or a radioactive signal, to provide ameans of detecting the binding of the candidate agent to TRPM4b. Thelabel also can be an enzyme, such as, alkaline phosphatase orhorseradish peroxidase, which when provided with an appropriatesubstrate produces a product that can be detected. Alternatively, thelabel can be a labeled compound or small molecule, such as an enzymeinhibitor, that binds but is not catalyzed or altered by the enzyme. Thelabel also can be a moiety or compound, such as, an epitope tag orbiotin which specifically binds to streptavidin. For the example ofbiotin, the streptavidin is labeled as described above, thereby,providing a detectable signal for the bound TRPM4b. As known in the art,unbound labeled streptavidin is removed prior to analysis.Alternatively, TRPM4b can be immobilized or covalently attached to asurface and contacted with a labeled candidate bioactive agent.Alternatively, a library of candidate bioactive agents can beimmobilized or covalently attached to a biochip and contacted with alabeled TRPM4b. Procedures which employ biochips are well known in theart.

In a preferred embodiment, the ion permeability of TRPM4b is measured inintact cells, preferably HEK-293 cells, which are transformed with avector comprising nucleic acid encoding TRPM4b and an inducible promoteroperably linked thereto. Endogenous levels of intracellular ions aremeasured prior to inducement and then compared to the levels ofintracellular ions measured subsequent to inducement. Fluorescentmolecules such as fura-2 can be used to detect intracellular ion levels.TRPM4b permeability to Na⁺, K⁺, and Cs⁺ and to other monovalent cationscan be measured in this assay.

In a preferred embodiment for screening for candidate bioactive agentswhich modulate expression levels of TRPM4b within cells, candidateagents can be used which wholly suppress the expression of TRPM4b withincells, thereby altering the cellular phenotype. In a further preferredembodiment, candidate agents can be used which enhance the expression ofTRPM4b within cells, thereby altering the cellular phenotype. Examplesof these candidate agents include antisense cDNAs and DNAs, regulatorybinding proteins and/or nucleic acids, as well as any of the othercandidate bioactive agents herein described which modulate transcriptionor translation of nucleic acids encoding TRPM4b.

In a further embodiment, candidate bioactive agents are used to openTRPM4b channels in a variety of cells such as cells of the nervous,immune, and muscular systems of vertebrates wherein the opening of theTRPM4b channels results in a decreased or reduced immune response invertebrates. Bioactive agents such as the ones described herein areuseful in the treatment of diseases, conditions associated withdiseases, or disorders, such autoimmune or graft versus host diseases,or other related autoimmune disorders, wherein the decreased or reducedimmune response results in an improved condition of the vertebrate(i.e., the disease, condition associated with the disease, or disorderis prevented, eliminated or diminished).

In still a further embodiment, candidate bioactive agents are used toclose TRPM4b channels in a variety of cells such as cells of thenervous, immune, and muscular systems of vertebrates wherein the closingof the TRPM4b channels results in an enhanced or augmented immuneresponse in vertebrates. Bioactive agents such as the ones describedherein are useful in the treatment of diseases, conditions associatedwith diseases, or disorders such as breast and colon cancer, or otherforms of cancer, wherein an enhanced or augmented immune responseresults in the improved condition of the vertebrate (i.e., the disease,condition associated with the disease, or disorder is prevented,eliminated or diminished).

In still another embodiment, the invention provides antibodies whichspecifically bind to unique epitopes on the TRPM4b polypeptide, e.g.unique epitopes of the protein comprising amino acids from 1 throughabout 1214 of SEQ ID NO:2 (FIG. 8).

The anti-TRPM4b polypeptide antibodies may comprise polyclonalantibodies. Methods of preparing polyclonal antibodies are known to theskilled artisan. Polyclonal antibodies can be raised in a mammal, forexample, by one or more injections of an immunizing agent and, ifdesired, an adjuvant. Typically, the immunizing agent and/or adjuvantwill be injected in the mammal by multiple subcutaneous orintraperitoneal injections. The immunizing agent may include the TRPM4bpolypeptide or a fusion protein thereof. It may be useful to conjugatethe immunizing agent to a protein known to be immunogenic in the mammalbeing immunized. Examples of such immunogenic proteins include but arenot limited to keyhole limpet hemocyanin, serum albumin, bovinethyroglobulin, and soybean trypsin inhibitor. Examples of adjuvantswhich may be employed include Freund's complete adjuvant and MPL-TDMadjuvant (monophosphoryl Lipid A, synthetic trehalose dicorynomycolate).The immunization protocol may be selected by one skilled in the artwithout undue experimentation.

The anti-TRPM4b polypeptide antibodies may further comprise monoclonalantibodies. Monoclonal antibodies may be prepared using hybridomamethods, such as those described by Kohler and Milstein, Nature,256:495(1975). In a hybridoma method, a mouse, hamster, or other appropriatehost animal, is typically immunized with an immunizing agent to elicitlymphocytes that produce or are capable of producing antibodies thatwill specifically bind to the immunizing agent. Alternatively, thelymphocytes may be immunized in vitro.

The immunizing agent will typically include the TRPM4b polypeptide or afusion protein thereof. Generally, either peripheral blood lymphocytes(“PBLs”) are used if cells of human origin are desired, or spleen cells,kidney cells, or lymph node cells are used if non-human mammaliansources are desired. The lymphocytes are then fused with an immortalizedcell line using a suitable fusing agent, such as polyethylene glycol, toform a hybridoma cell [Goding, Monoclonal Antibodies: Principles andPractice, Academic Press, (1986) pp. 59-103]. Immortalized cell linesare usually transformed mammalian cells, particularly myeloma cells ofrodent, bovine and human origin. Usually, rat or mouse myeloma celllines are employed. The hybridoma cells may be cultured in a suitableculture medium that preferably contains one or more substances thatinhibit the growth or survival of the unfused, immortalized cells. Forexample, if the parental cells lack the enzyme hypoxanthine guaninephosphoribosyl transferase (HGPRT or HPRT), the culture medium for thehybridomas typically will include hypoxanthine, aminopterin, andthymidine (“HAT medium”), which substances prevent the growth ofHGPRT-deficient cells.

Preferred immortalized cell lines are those that fuse efficiently,support stable high level expression of antibody by the selectedantibody-producing cells, and are sensitive to a medium such as HATmedium. More preferred immortalized cell lines are murine myeloma lines,which can be obtained, for instance, from the Salk Institute CellDistribution Center, San Diego, Calif. and the American Type CultureCollection, Rockville, Md. Human myeloma and mouse-human heteromyelomacell lines also have been described for the production of humanmonoclonal antibodies [Kozbor, J. Immunol., 133:3001 (1984); Brodeur etal., Monoclonal Antibody Production Techniques and Applications, MarcelDekker, Inc., New York, (1987) pp. 51-63].

The culture medium in which the hybridoma cells are cultured can then beassayed for the presence of monoclonal antibodies directed against aTRPM4b polypeptide. Preferably, the binding specificity of monoclonalantibodies produced by the hybridoma cells is determined byimmunoprecipitation or by an in vitro binding assay, such asradioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA).Such techniques and assays are known in the art. The binding affinity ofthe monoclonal antibody can, for example, be determined by the Scatchardanalysis of Munson and Pollard, Anal. Biochem., 107:220 (1980).

After the desired hybridoma cells are identified, the clones may besubcloned by limiting dilution procedures and grown by standard methods[Goding, supra ]. Suitable culture media for this purpose include, forexample, Dulbecco's Modified Eagle's Medium and RPMI-1640 medium.Alternatively, the hybridoma cells may be grown in vivo as ascites in amammal.

The monoclonal antibodies secreted by the subclones may be isolated orpurified-from the culture medium or ascites fluid by conventionalimmunoglobulin purification procedures such as, for example, proteinA-Sepharose, hydroxylapatite chromatography, gel electrophoresis,dialysis, or affinity chromatography.

The monoclonal antibodies may also be made by recombinant DNA methods,such as those described in U.S. Pat. No. 4,816,567. DNA encoding themonoclonal antibodies of the invention can be readily isolated andsequenced using conventional procedures (e.g., by using oligonucleotideprobes that are capable of binding specifically to genes encoding theheavy and light chains of murine antibodies). The hybridoma cells of theinvention serve as a preferred source of such DNA. Once isolated, theDNA may be placed into expression vectors, which are then transfectedinto host cells such as simian COS cells, Chinese hamster ovary (CHO)cells, or myeloma cells that do not otherwise produce immunoglobulinprotein, to obtain the synthesis of monoclonal antibodies in therecombinant host cells. The DNA also may be modified, for example, bysubstituting the coding sequence for human heavy and light chainconstant domains in place of the homologous murine sequences [U.S. Pat.No. 4,816,567; Morrison et al., supra] or by covalently joining to theimmunoglobulin coding sequence all or part of the coding sequence for anon-immunoglobulin polypeptide. Such a non-immunoglobulin polypeptidecan be substituted for the constant domains of an antibody of theinvention, or can be substituted for the variable domains of oneantigen-combining site of an antibody of the invention to create achimeric bivalent antibody.

The anti-TRPM4b polypeptide antibodies may further comprise monovalentantibodies. Methods for preparing monovalent antibodies are well knownin the art. For example, one method involves recombinant expression ofimmunoglobulin light chain and modified heavy chain. The heavy chain istruncated generally at any point in the Fc region so as to prevent heavychain crosslinking. Alternatively, the relevant cysteine residues aresubstituted with another amino acid residue or are deleted so as toprevent crosslinking. In vitro methods are also suitable for preparingmonovalent antibodies. Digestion of antibodies to produce fragmentsthereof, particularly, Fab fragments, can be accomplished using routinetechniques known in the art.

The anti-TRPM4b polypeptide antibodies may further comprise humanizedantibodies or human antibodies. Humanized forms of non-human (e.g.,murine) antibodies are chimeric immunoglobulins, immunoglobulin chainsor fragments thereof (such as Fv, Fab, Fab′, F(ab′)2 or otherantigen-binding subsequences of antibodies) which contain minimalsequence derived from nonhuman immunoglobulin. Humanized antibodiesinclude human immunoglobulins (recipient antibody) in which residuesfrom a complementary determining region (CDR) of the recipient arereplaced by residues from a CDR of a non-human species (donor antibody)such as mouse, rat or rabbit having the desired specificity, affinityand capacity. In some instances, Fv framework residues of the humanimmunoglobulin are replaced by corresponding nonhuman residues.Humanized antibodies may also comprise residues which are found neitherin the recipient antibody nor in the imported CDR or frameworksequences. In general, the humanized antibody will comprisesubstantially all of at least one, and typically two, variable domains,in which all or substantially all of the CDR regions correspond to thoseof a non-human immunoglobulin and all or substantially all of the FRregions are those of a human immunoglobulin consensus sequence. Thehumanized antibody optimally also will comprise at least a portion of animmunoglobulin constant region (Fc), typically that of a humanimmunoglobulin [Jones et al., Nature, 321:522-525 (1986); Riechmann etal., Nature, 332:323-329 (1988); and Presta, Curr. Op. Struct. Biol.,2:593596 (1992)].

Methods for humanizing non-human antibodies are well known in the art.Generally, a humanized antibody has one or more amino acid residuesintroduced into it from a source which is non-human. These non-humanamino acid residues are often referred to as “import” residues, whichare typically taken from an “import” variable domain. Humanization canbe essentially performed following the method of Winter and co-workers[Jones et al., Nature, 321:522-525 (1986); Riechmann et al., Nature,332:323-327 (1988); Verhoeyen et al., Science, 239:1534-1536 (1988)], bysubstituting rodent CDRs or CDR sequences for the correspondingsequences of a human antibody. Accordingly, such “humanized” antibodiesare chimeric antibodies (U.S. Pat. No. 4,816,567), wherein substantiallyless than an intact human variable domain has been substituted by thecorresponding sequence from a non-human species. In practice, humanizedantibodies are typically human antibodies in which some CDR residues andpossibly some FR residues are substituted by residues from analogoussites in rodent antibodies.

Human antibodies can also be produced using various techniques known inthe art, including phage display libraries [Hoogenboom and Winter, J.Mol. Biol., 227:381 (1991); Marks et al., J. Mol. Biol., 222:581(1991)]. The techniques of Cole et al. and Boerner et al., are alsoavailable for the preparation of human monoclonal antibodies (Cole etal., Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, p. 77(1985) and Boerner et al., J. Immunol., 147(1):86-95 (1991)]. Similarly,human antibodies can be made by the introducing of human immunoglobulinloci into transgenic animals, e.g. mice in which the endogenousimmunoglobulin genes have been partially or completely inactivated. Uponchallenge, human antibody production is observed, which closelyresembles that seen in humans in all respects, including generearrangement, assembly, and antibody repertoire. This approach isdescribed, for example, in U.S. Pat. Nos. 5,545,807; 5,545,806;5,569,825; 5,625,126; 5,633,425; 5,661,016, and in the followingscientific publications: Marks et al., Bio/Technology 10, 779-783(1992); Lonberg et al., Nature 368:856-859 (1994); Morrison, Nature368:812-13 (1994); Fishwild et al., Nature Biotechnology 14, 845-51(1996); Neuberger, Nature Biotechnology 14, 826 (1996); Lonberg andHuszar, Intern. Rev. Immunol. 13 65-93 (1995).

The anti-TRPM4b polypeptide antibodies, may further compriseheteroconjugate antibodies. Heteroconjugate antibodies are composed oftwo covalently joined antibodies. Such antibodies have, for example,been proposed to target immune system cells to unwanted cells [U.S. Pat.No. 4,676,980], and for treatment of HIV infection [WO 91/00360; WO92/200373; EP 03089]. It is contemplated that the antibodies may beprepared in vitro using known methods in synthetic protein chemistry,including those involving crosslinking agents. For example, immunotoxinsmay be constructed using a disulfide exchange reaction or by forming athioether bond. Examples of suitable reagents for this purpose includeiminothiolate and methyl-4-mercaptobutyrimidate and those disclosed, forexample, in U.S. Pat. No. 4,676,980.

In a further embodiment, the anti-TRPM4b polypeptide antibodies may havevarious utilities. For example, anti-TRPM4b polypeptide antibodies maybe used in diagnostic assays for TRPM4b polypeptides, e.g. detecting itsexpression in specific cells, tissues, or serum. Various diagnosticassay techniques known in the art may be used, such as competitivebinding assays, direct or indirect sandwich assays andimmunoprecipitation assays conducted in either heterogeneous orhomogeneous phases [Zola, Monoclonal Antibodies: A Manual of Techniques,CRC Press, Inc. (1987) pp. 147-158]. The antibodies used in thediagnostic assays can be labeled with a detectable moiety. Thedetectable moiety should be capable of producing, either directly orindirectly, a detectable signal. For example, the detectable moiety maybe a radioisotope, such as ³H, ¹⁴C, ³²P, ³⁵S, or ¹²⁵I, a fluorescent orchemiluminescent compound, such as fluorescein isothiocyanate,rhodamine, or luciferin, or an enzyme, such as alkaline phosphatase,beta-galactosidase or horseradish peroxidase. Any method known in theart for conjugating the antibody to the detectable moiety may beemployed, including those methods described by Hunter et al., Nature,144:945 (1962); David et al., Biochemistry, 13:1014 (1974); Pain et al.,J. Immunol. Meth., 40:219 (1981); and Nygren, J. Histochem. andCytochem., 30:407 (1982).

Further, TRPM4b antibodies may be used in the methods of the inventionto screen for their ability to modulate the permeability of TRPM4bchannels to monovalent cations.

EXAMPLES

Commercially available reagents referred to in the examples were usedaccording to manufacturer's instructions unless otherwise indicated.

Example 1 Cloning and Sequence Analysis of TRPM4b

The genetrapper II solution hybridization method (Life Technologies) wasused to isolate the TRPM4b cDNA. Three rounds of screening with threedifferent human cDNA libraries were performed: thirteen PCR-positivecolonies were obtained from the kidney library, all containing 3′fragments of the TRPM4b cDNA. Further 51-sequence was obtained from thespleen library. Using this supplementary 5′-segment to design newfishing oligonucleotides, another 8 PCR positive clones were isolatedfrom a prostate library with one single clone containing the longestORF, coding for the putative full-length TRPM4b.

Example 2 Northern Blot Analysis

Single-stranded probes were constructed with the NheI/EcoRI/KpnI 1 kbfragment of the human TRPM4b 3′-end. FirstChoice™ Northern Blot forhuman tissue were obtained from Ambion (Austin, Tex.) and for the celllines, 3 mg of polyA RNA per lane were used. The dUTP-labeled RNA probewas generated using a T7-directed RNA probe synthesis kit from Ambion.All hybridizations were performed according to the manufacture'sprotocols.

Example 3 Protein Methods

Full-length TRPM4b cDNA was cloned into a modified version of thepCDNA4/TO vector (Invitrogen) with an N-terminal Flag epitope tag. Thecorrect sequence of the full-length Flag-TRPM4b expression construct wasconfirmed by DNA sequencing. The Flag-TRPM4b cDNA in pCDNA4/T0 waselectroporated into HEK-293 cells previously transfected with thepCDNA6/TR construct for Tet-repressor expression. Cells were placedunder zeocin selection, and zeocin-resistant clones were screened fortetracycline-inducible expression of the Flag-tagged TRPM4b protein.Cell surface iodination with Na1251 (1 mCi) (Amersham Pharmacia Biotech,Piscataway, N.J.) was carried out by the lactoperoxidase method. Forimmunoprecipitation, cells (107/ml) were lysed for 30 min at 4° C. inTris buffer pH 7.5 containing 0.5% Triton X-100 (Bio-Rad, Hercules,Calif.) and proteases inhibitors. The Flag-tagged proteins wereimmunoprecipitated from cleared lysate by an anti-Flag antibody (Sigma,St. Louis, Mo.). In other experiments, anti-Cbl antibodies (Santa-CruzBiotechnology, Santa Cruz, Calif.) and anti-V5 tag (Invitrogen,Carlsbad, Calif.) were used. The immunoprecipitated proteins wereresolved by 6% SDS-PAGE and visualized by Enhanced Chemiluminescence(Amersham Pharmacia Biotech).

Example 4 Cell Culture and Electrophysiology

Wild type and tetracycline-inducible FMK-293 Flag-TRPM4b-expressingcells were cultured at 37° C./5% CO2 in DMEM supplemented with 10% FBSand 2 mM glutamine. The medium was supplemented with blasticidin (5μg/ml; Invitrogen) and zeocin (0.4 mg/ml; Invitrogen). Cells wereresuspended in media containing 1 μg/ml tetracycline (Invitrogen) 24hours before experiments. For patch-clamp experiments, cells were keptin a standard Ringer's solution (in mM): NaCl 145, KCl 2.8, CaCl2 1,MgCl2 2, glucose 10, Hepes.NaOH 10, pH 7.2. In some experiments, thissolution was modified such that all but 1 mM of NaCl was replaced bycholine-Cl (choline-based solution). In experiments where ATP was used,it was added at 1 mM of the Mg²⁺ salt and extracellular Ca²⁺concentration was raised to 2 mM. The standard pipette-filling solutionscontained (in mM): K-glutamate 145, NaCl 8, MgCl2 1, Cs-BAPTA 10, pH 7.2adjusted with KOH. In some experiments, [Ca²⁺]i was buffered to 0.1-1 RMby 10 mM BAPTA and appropriate concentrations of CaCl2 or leftunbuffered. For inside-out single-channel recordings, the patch wasexcised into a similar solution, except that KCl was used instead ofK-glutamate. All reagents were purchased from Sigma and dissolved in thestandard intracellular solution. Patch-clamp experiments were performedin the whole-cell configuration at 21-25° C. Data was acquired with“Pulse” software controlling an EPC-9 amplifier (HEKA, Lambrecht,Germany). Voltage ramps of 50 ms duration spanning the voltage range of−100 to +100 mV were delivered from a holding potential of 0 mV at arate of 0.5 Hz over a period of 200 to 400 seconds. When applicable,voltages were corrected for liquid junction potentials. Currents werefiltered at 2.9 kHz and digitized at 100 μs intervals. Capacitivecurrents and series resistance were determined and corrected before eachvoltage ramp. For analysis, the very first ramps prior to currentactivation were digitally filtered at 2 kHz, pooled and used forleak-subtraction of all subsequent current records. The low-resolutiontemporal development of currents at a given potential was extracted fromthe leak-corrected individual ramp current records by measuring thecurrent amplitudes at voltages of −80 mV or +80 mV. Single-channelrecordings were performed in the inside-out configuration and currentswere filtered and sampled as above. For display purposes, data recordswere digitally filtered and down-sampled to 100 Hz.

Example 5 Calcium Measurements

The cytosolic calcium concentration of individual patch-clamped orintact cells was monitored at a rate of 5 Hz with aphotomultiplier-based system using a monochromatic light source tuned toexcite fura-2 fluorescence at 360 and 390 nm for 20 ms each. Emissionwas detected at 450-550 nm with a photomultiplier, whose analog signalswere sampled and processed by X-Chart software (HEKA, Lambrecht,Germany). Fluorescence ratios were translated into free intracellularcalcium concentration based on calibration parameters derived frompatch-clamp experiments with calibrated calcium concentrations. Inpatch-clamp experiments, fura-2 was added to the standard intracellularsolution at 100 μM. Ester loading of intact cells was performed byincubating cells for 30-45 min in standard solution supplemented with 5μM fura-2-AM. Local perfusion of individual cells with ATP was achievedthrough a wide-tipped, pressure-controlled application pipette (3 [Lmdiameter) placed at a distance of 30 μm from the cell underinvestigation.

What is claimed is:
 1. A method comprising a. contacting a TRPM4bchannel with a candidate agent; wherein said TRPM4b is expressed in arecombinant cell, b. measuring the monovalent cationic permeability ofsaid TRPM4b channel after contacting with said candidate bioactiveagent; and c. comparing said monovalent cationic permeability of saidTRPM4b channel after contacting with said candidate bioactive agent withthe monovalent cationic permeability of said TRPM4b channel in theabsence of said candidate bioactive agent to determine whether saidbioactive agent modulates the monvalent cationic permeability of saidTRPM4b channel. wherein said TRPM4b has an amino acid sequencecomprising SEQ. ID No: 2and is impermeable to Ca²⁺.
 2. The method ofclaim 1 wherein said candidate bioactive agent increases said monovalentcationic permeability of said TRPM4b channel.
 3. The method of claim 1wherein said candidate bioactive agent decreases said monovalentcationic permeability of said TRPM4b channel.
 4. The method of claim 1wherein said monovalent cation is selected from the group consisting ofNa⁺, K⁺, and Cs⁺.
 5. A method comprising: a. providing a recombinantcell comprising a recombinant nucleic acid comprising nucleic acidencoding TRPM4b and an inducible promoter operably linked thereto whichis capable of expressing said TRPM4b, and wherein said recombinant cellfurther comprises a monovalent cation indicator; b. inducing saidinducible promoter present in said recombinant cell to express saidTRPM4b and form a TRPM4b channel; c. contacting said recombinant cellwith a monovalent cation and said candidate agent; and d. comparing theintracellular levels of said monovalent cation in said recombinant cellafter contacting with said monovalent cation and said candidatebioactive agent with the intracellular levels of said monovalent cationin the absence of contacting with said candidate bioactive agent todetermine whether said bioactive agent modulates the monvalent cationicpermeability of said TRPM4b channel wherein said TRPM4b has an aminoacid sequence comprising SEQ. ID No: 2and is impermeable to Ca² ⁺. 6.The method of claim 5 wherein said contacting is of said candidate agentfollowed by said monovalent cation.
 7. The method of claim 5 whereinsaid monovalent cation is selected from the group consisting of Na⁺, K⁺,and Cs⁺.
 8. The method of claim 5 wherein the modulating activityincreases said monovalent cation permeability of said TRPM4b channel. 9.The method of claim 5 wherein the modulating activity decreases saidmonovalent cation permeability of said TRPM4b channel.
 10. The method ofclaim 7 or 9 wherein said modulating activity alters the membranepotential of said recombinant cell.
 11. The method of claim 5 whereinsaid indicator comprises a fluorescent molecule.
 12. The method of claim11 wherein said fluorescent molecule comprises fura-2.
 13. A method formeasuring monovalent cation permeability of a TRPM4b channel, saidmethod comprising: a. providing a recombinant cell wherein said cellcomprises a recombinant nucleic acid which expresses TRPM4b and saidcell further comprises a monovalent cation indicator; b. contacting saidrecombinant cell with a monovalent cation which interacts with saidindicator to generate a signal; and c. comparing the intracellularlevels of said monovalent cation by detecting said indicator signal insaid recombinant cell after contacting with said monovalent cation andin the absence of contacting with said monovalent cation, wherein saidTRPM4b has an amino acid sequence comprising SEQ. ID No: 2and isimpermeable to Ca².
 14. The method of claim 13 wherein said indicatorcomprises a fluorescent molecule.
 15. The method of claim 13 whereinsaid fluorescent molecule comprises fura-2.
 16. The method of claim 13wherein said monovalent cation is selected from the group consisting ofNa⁺, K⁺, and Cs⁺.
 17. The method of claim 13 further comprisingcontacting said recombinant cell with a candidate bioactive agent. 18.The method of claim 17 wherein said modulating activity increases saidmonovalent cation permeability of said TRPM4b channel.
 19. The method ofclaim 17 wherein said modulating activity decreases said monovalentcation permeability of said TRPM4b channel.
 20. The method of claim 18or 19 wherein said modulating activity alters the membrane potential ofsaid recombinant cell.
 21. A method comprising: a. providing arecombinant cell wherein said cell comprises a recombinant nucleic acidwhich expresses TRPM4b to form a TRPM4b channel and wherein saidrecombinant cell further comprises a monovalent cation indicator; b.providing a cell comprising a monovalent cation indicator; c. contactingsaid recombinant cell and said cell with a candidate agent; d. comparingsaid intracellular monovalent cation levels present in said recombinantcell to said intracellular monovalent cation levels in said cell agentto determine whether said bioactive agent modulates the monvalentcationic permeability of said TRPM4b channel wherein said TRPM4 b has anamino acid sequence comprising SEQ. ID No: 2and is impermeable to Ca² ⁺.22. A method comprising: a. providing a recombinant cell capable ofexpressing a recombinant nucleic acid encoding a TRPM4b protein; b.contacting said cell with said candidate agent; and c. comparing theexpression of said TRPM4b protein or fragment thereof in saidrecombinant cell after contacting said recombinant cell with saidcandidate agent to said cell recombinant cell without contacting saidrecombinant cell with said candidate, wherein said TRPM4b has an aminoacid sequence comprising all or part of SEQ. ID No: 2and is impermeableto Ca² ⁺.
 23. The method of claim 22 wherein the comparing comprisescomparing the level of expression of TRPM4b in the presence of saidcandidate agent to the level of expression to endogenous TRPM4b levels.24. The method of claims 1, 5, 13 and 22, wherein said candidate agentcomprises a small molecule, protein, polypeptide or nucleic acid.